The purpose of this study is to identify compounds which induce point mutations, after metabolic activation by testicular tissues to mutagens in mammals. The topics are: (1) Screening of the literature for compounds which react with testicular tissue, (2) Development of protocols and determination of optimal conditions for the in vitro mutation experiments, (3) Characterization of the activation capacity of germinal tissue in vitro and (4) Correlation with a histochemical mutation system using sperm of male mice. As a result we found that AF-2, a nitrofuran, is activated in the soluble enzyme system and the microsomal fraction of rabbit testis-tissue.